JP2551558B2 - Air-fuel ratio control method for internal combustion engine - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an air-fuel ratio control method for an internal combustion engine.

BACKGROUND ART In order to purify exhaust gas of an internal combustion engine, improve fuel efficiency, etc., the oxygen concentration in the exhaust gas is detected by an oxygen concentration sensor,
There is known an air-fuel ratio control device that feedback-controls the air-fuel ratio of an air-fuel mixture supplied to an engine according to the output level of the oxygen concentration sensor. As this air-fuel ratio control device, an electromagnetic valve is provided in an intake secondary air supply passage communicating with the carburetor throttle valve downstream, and the opening degree of the electromagnetic valve, that is, the amount of intake secondary air supply is controlled according to the output level of the oxygen concentration sensor. There is an air-fuel ratio control device of an intake secondary air supply system for feedback control (for example, Japanese Patent Publication No. 55-3533).

In such a conventional air-fuel ratio control device, it is determined from the output level of the oxygen concentration sensor whether the air-fuel ratio of the supply air-fuel mixture is lean or rich with respect to the target air-fuel ratio, and according to the determination result. In general, PI (proportional integration) control is performed in which the air-fuel ratio control value is increased or decreased by a proportional amount or an integral amount every predetermined period, and the intake secondary air supply amount is controlled according to the air-fuel ratio control value.

By the way, it is common that the reference value set by the base air-fuel ratio of the carburetor deviates from a predetermined value due to aging of the carburetor, or deterioration, and the standard air-fuel ratio does not correspond to the target air-fuel ratio, resulting in an error. Is. Therefore, there is a system in which the learning control for calculating the reference correction value for correcting the error of the reference value in a predetermined stable operating state and storing the new reference correction value is performed to improve the air-fuel ratio control accuracy.

However, in high altitudes, the intake air weight decreases as the intake air density decreases, and the base air-fuel ratio of the carburetor tends to become rich.Therefore, it is acceptable to correct the reference value with the reference correction value calculated by learning control. However, there is a problem in that sufficient air-fuel ratio control accuracy cannot be obtained and exhaust purification performance deteriorates or engine output decreases.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an air-fuel ratio control method for an internal combustion engine, which is capable of obtaining good exhaust gas purification performance at high altitudes and preventing a decrease in engine output.

The air-fuel ratio control method for an internal combustion engine according to the present invention is characterized in that the reference correction value is corrected and calculated according to the change amount with respect to the atmospheric reference pressure and the change amount with respect to the unit change amount of the atmospheric pressure.

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings.

In the air-fuel ratio control device of the intake secondary air supply system for a vehicle-mounted internal combustion engine to which the air-fuel ratio control method of the present invention shown in FIG. 1 is applied, intake air is supplied from the air intake port 1 to the air cleaner 2, the carburetor 3, and It is supplied to the engine 5 via the intake manifold 4. The vaporizer 3 is provided with a throttle valve 6, and a venturi 7 is formed upstream of the throttle valve 6.

The intake manifold 4 and the vicinity of the air outlet of the air cleaner are connected by an intake secondary air supply passage 8.
A linear solenoid valve 9 is provided in the intake secondary air supply passage 8. The opening degree of the solenoid valve 9 changes in proportion to the current value supplied to the solenoid 9a.

On the other hand, 10 is an absolute pressure sensor which is provided in the intake manifold 4 and generates an output of a level corresponding to the absolute pressure in the intake manifold 4, and 11 generates a pulse in accordance with the rotation of a crankshaft (not shown) of the engine 5. A crank angle sensor 12 for generating a cooling water temperature sensor for generating an output of a level corresponding to the cooling water temperature of the engine 5; and 14 provided in an exhaust manifold 15 of the engine 5 for generating an output voltage corresponding to the oxygen concentration in the exhaust gas. It is an oxygen concentration sensor. Oxygen concentration sensor
A catalytic converter 33 is provided in the exhaust manifold 15 downstream of the disposition position of 14 in order to promote reduction of harmful components in the exhaust gas. Solenoid valve 9, absolute pressure sensor 10, crank angle sensor 11, water temperature sensor 12, and oxygen concentration sensor 14
Is connected to the control circuit 20. The control circuit 20 further includes a vehicle speed sensor 16 for generating an output of a level corresponding to the speed of the vehicle.
And a throttle valve opening sensor 17 which is composed of a potentiometer and produces an output of a level corresponding to the opening of the throttle valve 6, and an atmospheric pressure sensor 18 which produces an output of a level corresponding to the atmospheric pressure. .

As shown in FIG. 2, the control circuit 20 is a level conversion circuit for converting the output levels of the absolute pressure sensor 10, the water temperature sensor 12, the oxygen concentration sensor 14, the vehicle speed sensor 16, the throttle valve opening sensor 17 and the atmospheric pressure sensor 18. 21 and a multiplexer 22 that selectively outputs one of the sensor outputs that have passed through the level conversion circuit 21.
A / D converter 23 for converting the signal output from the multiplexer 22 into a digital signal, and the crank angle sensor 1
A waveform shaping circuit 24 that shapes the output signal of 1 and a counter that measures the generation interval of the TDC signal output as a pulse from the waveform shaping circuit 24 by the number of clock pulses output from a clock pulse generation circuit (not shown). 25, a drive circuit 28 for driving the solenoid valve 9 to open, a CPU (central processing circuit) 29 for performing digital calculation according to a program,
RO with various processing programs and data written in advance
It consists of M30 and RAM31. Solenoid of solenoid valve 9
9a is connected in series with a drive transistor of the drive circuit 28 and a current detection resistor (both not shown), and a power supply voltage is supplied between both ends of the series circuit. Multiplexer 22, A / D
Converter 23, counter 25, drive circuit 28, CPU 29, ROM 30 and
The RAMs 31 are connected to each other by the input / output bus 32.

In such a configuration, information on the absolute pressure in the intake manifold 4, the cooling water temperature, the oxygen concentration in the exhaust gas, the vehicle speed, the throttle valve opening, and the atmospheric pressure is selectively supplied from the A / D converter 23, and the counter 25 Information indicating the engine speed from CPU29
Are respectively supplied to the input / output bus 32. The CPU 29 calculates the supply current value D _OUT to the solenoid 9a of the solenoid valve 9 as data by executing the processing program at every predetermined cycle T ₁ (for example, 50 m sec) as described later, and the calculated supply current value D _OUT is supplied to the drive circuit 28. The drive circuit 28 performs a closed loop control of the current value flowing in the solenoid 9a so that the current value flowing in the solenoid 9a becomes the supply current value D _OUT .

Next, the procedure of the air-fuel ratio control method according to the present invention will be described in detail with reference to the operation flow charts of the CPU 29 shown in FIGS. 3 and 4.

As shown in FIG. 3, the CPU 29 first reads the intake absolute pressure, the cooling water temperature, the engine speed, the oxygen concentration, and the atmospheric pressure (step 51), and determines whether or not the activation of the oxygen concentration sensor is completed. (Step 52). When the activation of the oxygen concentration sensor is completed, it is determined whether the cooling water temperature Tw is lower than the predetermined temperature Tw ₁ (step 53). If Tw <Tw ₁ , the engine has not been warmed up and is in a low temperature state, so the supply current value D _OUT is set to 0 (step 54). Tw
If ≧ Tw ₁ , the engine is not at a low temperature, so the change amount ΔP _A between the atmospheric pressure P _A read this time and the reference pressure P _A ref (for example, 760 mmHg) is calculated (step 55), and the absolute pressure P _BA and the engine rotation speed are calculated. The reference current value D _BASE of the supply current value to the solenoid valve 9 that is the reference value is set according to the number Ne (step 56), and the unit pressure change amount per unit atmospheric pressure change amount is set according to the absolute value P _BA and the engine speed Ne. The change amount ΔD of the reference current value D _BASE is set (step 57). As shown in FIG. 5, the ROM 30 has a reference current value D _{BASE that} is determined from the absolute value P _BA and the engine speed Ne as a D _BASE data map, and has the characteristics (shaded areas) shown in FIG. The amount of change ΔD determined from P _BA and the engine speed Ne is written in advance as a ΔD data map, so the CPU 29 reads the absolute pressure P _BA and the engine speed Ne.
The reference current value D _BASE corresponding to and is retrieved from the D _BASE data map, and the absolute pressure P _BA and engine speed N read
The amount of change ΔD corresponding to e is retrieved from the ΔD data map. After setting the reference current value D _BASE and the amount of change ΔD, it is determined whether or not the operating state of the vehicle (including the operating state of the engine) satisfies the air-fuel ratio feedback (F / B) control condition (step 58). . This determination is determined from the absolute pressure in intake manifold P _BA , the cooling water temperature Tw, the vehicle speed V, the throttle valve opening θth, and the engine speed Ne. For example, the air-fuel ratio feedback control condition is satisfied at low vehicle speed and low engine speed. It is supposed to not. If it is determined that the air-fuel ratio feedback control condition is not satisfied, the correction coefficient Kref corresponding to the intake manifold absolute pressure P _BA and the engine speed Ne is retrieved from the data map (step 59). Correction coefficient Kr
ef is a correction coefficient for correcting the error of the reference current value D _BASE due to the aging of the vaporizer. As shown in FIG. 7, the correction coefficient Kref for each area corresponding to the absolute value P _BA and the engine speed Ne is written in the RAM 31 as a Kref data map, so the CPU 29 reads the absolute pressure P _BA and the engine speed. The correction coefficient Kref corresponding to the number Ne is searched from the Kref data map. Search for the correction coefficient Kref
D _OUT is calculated by the following formula (step 60).

D _OUT = D _BASE × Kref × K _R + ΔP _A × ΔD (1) Here, K _R is the enrichment coefficient.

On the other hand, if the air-fuel ratio feedback control condition is satisfied, the air-fuel ratio feedback control routine is executed to calculate the supply current value D _OUT (step 61). Steps 54, 6
0, or by setting the supply current value D _OUT at 61, to output a supply current value D _OUT to the drive circuit 28 (Step 6
2).

The drive circuit 28 detects the value of the current flowing in the solenoid 9a of the solenoid valve 9 by the current detection resistor, compares the detected current value with the supply current value D _OUT, and turns on / off the drive transistor according to the comparison result. Supply current to the solenoid 9a. Therefore, a current having a supply current value D _OUT flows through the solenoid 9a, and the amount of intake secondary air proportional to the value of the current flowing through the solenoid 9a is supplied into the intake manifold 4. When the supply current value _DOUT is 0, the solenoid valve 9 closes and the supply of the intake secondary air is stopped.

Next, in the air-fuel ratio feedback control routine, as shown in FIG. 4, it is first determined whether or not the oxygen concentration is leaner than the reference concentration corresponding to the target air-fuel ratio, that is, the output level L _{O2 of the} oxygen concentration sensor 14. It is determined whether is smaller than the reference value Lref (step 71). If L _O2 <Lref, the air-fuel ratio is leaner than the target air-fuel ratio, so it is determined whether or not the air-fuel ratio flag F _AF indicating the determination result of the previous step 71 is 1 (step 72). If F _AF = 0, it is determined that the previous air-fuel ratio is rich, and since the air-fuel ratio was reversed from rich to lean, the proportional control component P _L is subtracted from the air-fuel ratio correction coefficient K _O2, and the calculated value is the current correction coefficient K _O2. Then, the air-fuel ratio flag F _AF is set equal to 1 (step 74). If F _AF = 1, it was determined that the air-fuel ratio was lean last time, so the integral control amount I _L is subtracted from the air-fuel ratio correction coefficient K _O2 and the calculated value is set as the current correction coefficient K _O2 (step 75). . On the other hand, in step 71, L _O2 ≧ Lref
If so, since the air-fuel ratio is richer than the target air-fuel ratio, it is determined whether the air-fuel ratio flag F _AF is 0 (step 7).
6). If F _AF = 1, it is determined that the previous air-fuel ratio was lean and the lean-to-rich reverse operation has been performed.
The proportional control amount P _R is added to K _O2 , the calculated value is set as the current correction coefficient K _O2 (step 77), and the air-fuel ratio flag F _AF is set equal to 0 (step 78). If F _AF = 0, it was determined that the air-fuel ratio was rich last time as well, so the air-fuel ratio correction coefficient K _O2
Integral control component I _R is added to and the calculated value is
_Set to _O2 (step 79). After the execution of step 74 or 78, the correction coefficient Kref corresponding to the intake manifold absolute pressure P _BA and the engine speed Ne is searched from the Kref data map (step 80) and corrected by the following equation using the searched correction coefficient Kref. The coefficient Kref is calculated (step 81).

When the correction coefficient Kref is calculated, the calculated correction coefficient Kref is written in a region corresponding to the absolute pressure P _BA and the engine speed Ne of the Kref data map (step 82). Then, the supply current value D _OUT is calculated by the following equation (step 83).

D _OUT = D _BASE × K _O2 + ΔP _A × ΔD (3) On the other hand, step 75 or 79 is immediately executed in step 83.
To calculate the supply current value D _OUT .

Figure 8 shows the relationship between the reference current value D _BASE when the corrected atmospheric pressure and the supply current value D _OUT, the reference current value D _BASE
On the other hand, the value obtained by adding the altitude change ΔP _A × ΔD becomes the supply current value D _OUT that can control the air-fuel ratio to the target air-fuel ratio.

In the embodiment of the present invention described above, the step
At 57, the change amount ΔD of the reference current value D _BASE per unit pressure change amount was searched from the data map according to the absolute pressure P _BA and the engine speed Ne, but (Ne / 1500 rpm) × (P _BA / 350mmH
It may be calculated from the equation g) × K ₁ .

EFFECTS OF THE INVENTION As described above, in the air-fuel ratio control method of the present invention, the reference correction value is corrected and calculated according to the change amount with respect to the atmospheric reference pressure and the change amount of the reference value with respect to the unit change amount of atmospheric pressure. It is possible to correct the rich ratio of the base air-fuel ratio of the carburetor in the above, and to improve the air-fuel ratio control accuracy. Therefore, it is possible to prevent a decrease in engine output at high altitudes and obtain good exhaust gas purification performance.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an apparatus to which the air-fuel ratio control method of the present invention is applied, FIG. 2 is a block diagram showing a specific configuration of a control circuit in the apparatus of FIG. 1, and FIGS. 3 and 4 are Flow chart showing the operation of the CPU, Figure 5 shows the D _BASE data map,
FIG. 6 is a diagram showing an absolute pressure P _BA -engine speed Ne-change amount ΔD characteristic, FIG. 7 is a diagram showing a Kref data map, and FIG.
The figure is a diagram showing the relationship between the reference current value D _BASE and the supply current value D _OUT when the atmospheric pressure is corrected. Explanation of symbols of main parts 2 …… Air cleaner 3 …… Vaporizer 4 …… Intake pipe 6 …… Throttle valve 7 …… Venturi 8 …… Intake secondary air supply passage 9 …… Linear solenoid valve 10 …… Absolute pressure Sensor 11 …… Crank angle sensor 12 …… Cooling water temperature sensor 14 …… Oxygen concentration sensor 15 …… Exhaust pipe 17 …… Throttle valve opening sensor 33 …… Catalytic converter

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Atsushi Atsushi 1-4-1, Chuo, Wako-shi, Saitama, Honda R & D Co., Ltd. (56) References JP-A-60-93150 (JP, A) JP-A-SHO 57-148039 (JP, A)

Claims (2)

(57) [Claims] 1. An internal combustion engine having an exhaust component concentration sensor for producing an output according to an exhaust component concentration in exhaust gas in an exhaust system, wherein a reference value for air-fuel ratio control is set in accordance with a plurality of engine operating parameters related to engine load. Set, and when the air-fuel ratio feedback control condition is satisfied, the output value of the exhaust gas component concentration sensor is compared with the target value every predetermined period, and the air-fuel ratio correction value is set according to the comparison result, and at least the exhaust gas component is set. If the output value of the concentration sensor is inverted with respect to the target value, a reference correction value for correcting the error of the reference value is calculated, and the set reference value is corrected according to the air-fuel ratio correction value to obtain the target. An air-fuel ratio control method for determining an output value for an air-fuel ratio and adjusting the air-fuel ratio of an air-fuel mixture supplied to an engine according to the output value, wherein the reference correction value is set to an atmospheric reference pressure. Air-fuel ratio control method and calculating by the correction according to the amount of change in the reference value for a unit change amount of the change amount and atmospheric pressure. 2. An air-fuel ratio control method, wherein each time the reference correction value is calculated, the reference correction value is stored in association with each value of the plurality of engine operating parameters.